My aunt had a 69 Olds Cutlass she insisted got Quaker State oil changes ever 6,000 miles. Around 50,000 I had to replace all the rocker stands. The motor was so sledged up, the rockers left an imprint in the crud stuck to the inside of the covers. I had to do the whole deal again at around 70,000. I finally convinced her she needed to quit using Quaker State, and she needed to change her oil at 2,000 miles instead of 6,000 miles. After following my advice, she did get over 100K miles out of that poor Olds before she traded it on something else. Gene